The present invention relates to an image forming apparatus represented by, for example, an electro-photographic type electronic copying machine and a printer.
In general, an image forming apparatus is constructed as follows. Specifically, a toner image is formed by an image forming unit consisting of a photosensitive body and a developing device. The formed toner image is transferred onto a transfer medium such as a paper sheet or a transparent resin sheet for an overhead projector, which is transferred by a transfer belt. The transfer medium having the toner image transferred thereonto is heated so as to fix the toner image to the transfer medium.
In the image forming apparatus of the construction described above, the photosensitive body is rotated in general at a predetermined peripheral speed by a DD (Direct Drive) motor. However, it is known to the art that, where the DD motor is rotated at an angular speed not higher than, for example, 80 rpm, the angular rotating speed is changed by the cogging component inherent in the motor. In order to lower the influence given by the cogging component, a method of mounting a fly-wheel to the rotary shaft of the motor is widely employed for increasing the inertia moment. However, it is difficult to remove completely the fluctuation of the rotation.
Also, in the image forming apparatus, the load fluctuation is generated when, for example, the transfer medium enters or passes through the region between the photosensitive body and the transfer belt so as to bring about jitter in the formed toner image.
It is known to the art that, since the constant parameter of the compensation circuit for controlling the rotation of the DD motor is fixed to a predetermined value, the fluctuation of the rotation referred to above is generated by the nonuniformity of the motor constant (coil or magnetization) or by the influence produced by the load fluctuation.
Various measures are proposed to date in order to suppress the jitter occurrence. For example, it is proposed in Japanese Patent Disclosure (Kokai) No. 5-191605 that the driving period of a stepping motor for rotating the photosensitive drum is aligned with the period of the light exposure timing (light-emitting timing of a laser element) of the light exposure device. Also, it is proposed in Japanese Patent Disclosure (Kokai) No. 8-160692 that the gear ratio in the motor driving section is made an integer number times as much as the reference frequency of the stepping motor. Further, it is proposed in Japanese Patent Disclosure (Kokai) No. 11-65222 that the rotating speed fluctuation of the photosensitive body is reflected in the transfer belt by utilizing a regenerative electromotive force of the motor so as to suppress the load fluctuation.
However, it is difficult to remove completely the jitter contained in the toner image by any of the motor control methods proposed in the prior arts referred to above.
An object of the present invention is to provide an image forming apparatus, which permits optimizing the drive control of the motor so as to suppress the jitter occurrence in the toner image caused by the fluctuation in the rotating speed of the photosensitive body, which is caused by the load fluctuation.
Another object of the present invention is to provide an image forming apparatus, which permits suppressing the jitter occurrence by using a servo compensation system, in which the parameter constant used for driving the motor is made programmable, so as to make the circuit constant for the compensation system manually changeable in the direction in which the detected error in the rotating speed is made smaller.
A still another object of the present invention is to provide an image forming apparatus, which permits suppressing the jitter occurrence by using a servo compensation system, in which the parameter constant used for driving the motor is made programmable, so as to make the circuit constant for the compensation system automatically changeable in the direction in which the detected error in the rotating speed is made smaller.
According to a first aspect of the present invention, there is provided an image forming apparatus, comprising:
a first motor for rotating a photosensitive member at a predetermined speed;
a second motor for transferring a transfer medium onto which the toner image formed on the photosensitive member is transferred at a speed equal to the moving speed of the photosensitive member;
a third motor for supplying the transfer medium toward the photosensitive member at a predetermined speed;
a driving device supplying driving signals to the first, second and third motors;
a detecting mechanism for detecting the occurrence of a phenomenon for changing the magnitude of the driving signals supplied from the driving device to the first, second and third motors; and
an input device for changing the magnitude of the driving signals supplied from the driving device to the first, second and third motors on the basis of the occurrence of the phenomenon detected by the detecting mechanism.
According to a second aspect of the present invention, there is provided an image forming apparatus, comprising:
a first motor for rotating a photosensitive member at a predetermined speed;
a second motor for transferring a transfer medium onto which the toner image formed on the photosensitive member is transferred at a speed equal to the moving speed of the photosensitive member;
a third motor for supplying the transfer medium toward the photosensitive member at a predetermined speed;
a driving device supplying driving signals to the first, second and third motors;
a detecting mechanism for detecting the occurrence of a phenomenon for changing the magnitude of the driving signals supplied from the driving device to the first, second and third motors; and
a control amount setting mechanism for setting the magnitude of the driving signals supplied from the driving device to the first, second and third motors on the basis of the occurrence of the phenomenon detected by the detecting means.
Further, according to a third embodiment of the present invention, there is provided a method of setting the image forming conditions of an image forming apparatus, in which the magnitude of the jitter contained in the toner image formed in the image forming apparatus is detected and the image forming conditions are set in a manner to minimize the magnitude of the jitter, comprising the steps of:
monitoring the fluctuation in the magnitude of the motor current supplied from a motor driving device for driving a first motor to the first motor so as to detect the fluctuation in the rotating speed of the first motor;
operating a second motor for transferring a transfer medium onto which the toner image formed the photosensitive body is transferred at a speed equal to the moving speed of the photosensitive body and a third motor for supplying the transfer medium toward the photosensitive body at a predetermined speed; and
setting the magnitude and the phase of the motor current supplied to the motor driving device so as to minimize the fluctuation in the rotating speed of the first motor.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.